In an aircraft gas turbine engine, a large number of sensors are provided in various parts thereof and the output values of these sensors are used for optimally controlling the operation of the engine. A fault in any one of such sensors may cause abnormal values in the control parameters, and prevents satisfactory operation of the engine. Therefore, it is highly important to take appropriate measures in case of a sensor failure.
A fault of a sensor can be detected in come cases by comparing the output value of the sensor with a certain limit value or the change rate of the output value of the sensor with a prescribed threshold value. See Japanese patent laid-open publication No. 6-264767, for instance.
However, this known technology is only suitable for detecting misfire when starting the engine, and is not suitable for promptly detecting a fault in a sensor during the normal steady-state and transient operation of the engine. Also, to permit detection of an abnormal output of each one of a large number of sensors, a same number of reference maps as the number of the sensors are required for evaluating every one of the sensors. This undesirably increases the complexity of the control program.
In the case of a gas turbine engine including a high pressure shaft and a low pressure shaft that are disposed in a coaxial relationship, it is also known to define a prescribed relationship between the rotational speeds of the high pressure shaft and low pressure shaft, and judge that at least one of the sensors is faulty when the output values of the rotational speed sensors for the high pressure shaft and low pressure shaft deviate from the prescribed relationship beyond a certain threshold. See Japanese patent laid open publication No. 2000-249629.
Again, this known technology is capable of achieving any reliability only in a limited operating range, and is unable to detect a fault in the sensors in the high speed and/or transient operating mode of the engine.